2016 Update

Task/N-queens-problem/Rust/n-queens-problem-2.rust

@@ -0,0 +1,77 @@
+use std::collections::LinkedList;
+use std::iter::IntoIterator;
+
+fn main() {
+    for (n, s) in NQueens::new(8).enumerate() {
+        println!("Solution #{}:\n{}\n", n + 1, s.to_string());
+    }
+}
+
+fn permutations<'a, T, I>(collection: I) -> Box<Iterator<Item=LinkedList<T>> + 'a>
+    where I: 'a + IntoIterator<Item=T> + Clone,
+          T: 'a + PartialEq + Copy + Clone {
+    if collection.clone().into_iter().count() == 0 {
+        Box::new(vec![LinkedList::new()].into_iter())
+    }
+    else {
+        Box::new(
+            collection.clone().into_iter().flat_map(move |i| {
+                permutations(collection.clone().into_iter()
+                    .filter(move |&i0| i != i0)
+                    .collect::<Vec<_>>())
+                    .map(move |mut l| {l.push_front(i); l})
+            })
+        )
+    }
+}
+
+pub struct NQueens {
+    iterator: Box<Iterator<Item=NQueensSolution>>
+}
+
+impl NQueens {
+    pub fn new(n: u32) -> NQueens {
+        NQueens {
+            iterator: Box::new(permutations(0..n)
+                .filter(|vec| {
+                    let iter = vec.iter().enumerate();
+                    iter.clone().all(|(col, &row)| {
+                        iter.clone().filter(|&(c,_)| c != col)
+                            .all(|(ocol, &orow)| {
+                            col as i32 - row as i32 !=
+                                ocol as i32 - orow as i32 &&
+                            col as u32 + row != ocol as u32 + orow
+                        })
+                    })
+                })
+                .map(|vec| NQueensSolution(vec))
+            )
+        }
+    }
+}
+
+impl Iterator for NQueens {
+    type Item = NQueensSolution;
+    fn next(&mut self) -> Option<NQueensSolution> {
+        self.iterator.next()
+    }
+}
+
+pub struct NQueensSolution(LinkedList<u32>);
+
+impl ToString for NQueensSolution {
+    fn to_string(&self) -> String {
+        let mut str = String::new();
+        for &row in self.0.iter() {
+            for r in 0..self.0.len() as u32 {
+                if r == row {
+                    str.push_str("Q ");
+                } else {
+                    str.push_str("- ");
+                }
+            }
+            str.push('\n');
+        }
+        str
+    }
+}